A. Field of the Invention
The present invention relates generally to the field of servo control and more particularly to a servo control arrangement utilizing alternately energized light sources and a single photodetector to accurately detect the position of a coded aperture member movable with a controlled member and to provide feedback control signals for controlling the position of the controlled member.
B. Description of the Prior Art
Various control apparatus are known for slide projectors to control the positioning of a slide tray to a slide position. Control arrangements of this type are disclosed in U.S. Pat. Nos. 3,296,727, 3,225,652, 3,299,554, 3,895,864, 3,907,414, 3,924,942, 4,041,457, 3,644,027, 3,510,215, 3,733,122, 3,652,155, 3,623,803, 3,700,320 and 3,732,546.
In U.S. Pat. Nos. 3,907,414, and 3,895,864, the slide position of the slide tray is detected by the use of an optically coded disc 24 with absolute position address and coding provided by six concentric optically coded rings. The disc also includes optically coded stop control portions on an outer concentric ring with one opitcal transparent portion for each slide portion of the linear tray array.
U.S. Pat. No. 4,041,457 discloses the positioning of slides by a digitally controlled servo motor; the servo motor being controlled by the output of a comparator.
While the above-described control arrangements of the prior art are generally suitable for their intended use, it would be desirable to more accurately control the positioning of a movable member to one of a plurality of positions.